In the manufacture of bevel and hypoid gears with curved flank lines, the cutting tools utilized are primarily face mill or face hob cutters, such types of cutting tools are well known in the art of gear manufacture. In face mill cutters the cutting blades are arranged in the cutter head such that one tooth slot is formed with each plunge of the cutter and the cutter must be withdrawn and the workpiece indexed to the next tooth slot position in order to form the next tooth slot.
Face hobbing comprises cutting blades arranged about a cutter, not in line with each other, but in groups, usually pairs comprising an inner cutting blade and an outer cutting blade. Unlike most face milling processes, in which all cutting blades pass through the tooth slot during its formation, face hobbing comprises each successive group of cutting blades passing through respective successive tooth slot with each blade in the group forming a cut completely along the longitudinal portion of the tooth slot. The cutter and the workpiece rotate in a timed relationship with each other thereby allowing continual indexing of the workpiece and continual formation of each tooth slot of the gear. Thus, in face hobbing, a single plunge of the cutting tool results in all tooth slots of the workpiece being formed.
Cutting tools for face mill and face hob processes usually consist of disk-shaped cutter heads with stick-type cutting blades, made from bar stock tool steel for example, which are inserted and positioned in slots formed in the cutter heads. Each cutting blade comprises a front rake face, cutting edge, a cutting side surface oriented at a predetermined relief angle, clearance edge, clearance side surface, and a top surface. Examples of inserted stick-type cutter heads and blades are shown in U.S. Pat. Nos. 4,575,285 to Blakesley and 4,621,954 to Kitchen et al.
To have each blade of one kind, especially inner or outer blades, producing the same chip thickness and therefore having the same load and wear, the radial location of the cutting edge is most important. Tolerances of the blade shank and the cutting edge location relative to the shank as well as tolerances of "wear" of the slots in the cutter head can add up.
One method of measuring and truing both face milling and face hobbing cutters to correct radial location errors of cutting blades is disclosed in International Patent Application Publication No. WO 97/07930 in the name of The Gleason Works (Stadtfeld). In this method, the cutting side relief surface of the cutting blade is positioned substantially parallel to the offset travel direction of a probe. The cutting side relief surface is probed to determine the radial position of the cutting side and the position is recorded. The recorded position is compared with a predetermined position.
However, while the radial position of a cutting blade is important in both face milling and face hobbing operations, the position of the front face (index position) of a cutting blade is also important in face hobbing processes. This can be understood when the timed relationship between the rotating tool and rotating workpiece is considered. If a cutting blade is not in its proper position (index position) with respect to other like blades in the cutter head, the cutting blade will arrive either early or late to its respective tooth slot. As such, the chips removed from the tooth slot will be either thicker or thinner than those produced by other cutting blades in other tooth slots thus introducing uneven load and wear in the cutting tool.
It is an object of the present invention to provide a method of determining the amount of indexing error that exists in a face hobbing cutter.
It is another object of the present invention to provide a manner by which to adjust the cutting blades to account for any determined index error.